This invention relates to a process for the production of elastomeric, primarily syndiotactic polymers and to a catalyst which can be used in such process.
Syndiotactic polypropylene is prepared traditionally near dry ice temperature as described by G. Natta et al., U.S. Pat. No. 3,335,121, Aug. 6, 1967 to Montecatini Edison, in extremely low yield (giving product containing only 40 to 80% low molecular weight short block length, syndiotactic polymer) using soluble vanadium chloride or ketonate complexes in conjunction with dialkyl aluminum halides. As measured by triads in the .sup.13 C NMR, a polymerization which produces 76% syndiotactic and 0% isotactic polymer at -78.degree. C. will produce polymer which is only 15% syndiotactic and 59% isotactic when carried out at 41.degree. C., Y. Doi, M. Takada and T. Keii, Makromol. Chem. 180, 57-64 (1979). The most active catalyst claimed to date uses vanadium tris(2-methyl-3-oxobutanalate) with 400 equivalents of diethylaluminum chloride at -70.degree. C. to produce 79% syndiotactic polymer at a rate of 5.2 g/mmol vanadium/hour (0.08 g PP/g total catalyst) S. Suzuki EP 0206753 A1 , Dec. 30, 1986 to Toa Nenryo. In order to allow for a rapid characterization of syndiotactic polypropylene, an IR syndiotactic crystallinity index has been arbitrarily defined as the ratio 2A.sub.11.53 /[A.sub.2.32 +A.sub.2.35 ]. According to the above-mentioned Natta patent, syndiotactic polypropylenes produced using heterogeneous catalysts exhibit IR indices of less than 0.8. Youngman and Boor reported a 66% crystalline syndiotactic polymer to exhibit an index of 2.4, E. Youngman and J. Boor, Macromol. Rev. 2, 33-69 (1967).
Another patent to J. Collette and C. Tullock, U.S. Pat. No. 4,335,225, Jun. 15, 1982 to du Pont, claims significant yields of short stereoblock isotactic polymer to result from using homogeneous zirconium or hafnium catalysts supported upon partially hydrated alumina. The patent actually appears to be similar, using a different catalyst, to Natta's earlier stereoblock patent, U.S. Pat. No. 3,175,999, Mar. 30, 1965 to Montecatini. Thus an aged slurry of one gram of alumina plus 0.36 mmol of tetraneophylzirconium in 40 ml of cyclohexane and 2 ml of toluene was used together with 70 mmol of hydrogen to polymerize 126 grams of propylene dissolved in 450 ml cyclohexane at a temperature of about 51.degree. C. for an hour. The viscous product was washed thoroughly with acetone to give a crumb-like solid in yield of 284 g PP/mmol Zr/hour (84 g PP/g total catalyst). It was reported that some syndiotactic polymer was also present.
The specific catalyst Ti(OR).sub.4 /3TiCl.sub.3 *AlCl.sub.3 /R.sub.2 AlX has been reported to be effective for the production of high molecular weight rubbery materials from propylene by A. Schrage and E. Pless in U.S. Pat. No. 3,329,741, Jul. 4, 1967 to Rexall Drug. Productivities as high as 9.0 g PP/mmol Ti/hr (1.8 g PP/g total catalyst) are reported. Highly dispersed "quasihomogeneous" PR.sub.3 /3TiCl.sub.3 *AlCl.sub.3 /AlR'.sub.3, is reported to be utilized in aromatic solvent below 30.degree. C., for the production of low quality syndiotactic polypropylene by D. Emrick in U.S. Pat. No. 3,364,190, Jan. 16, 1968 to Standard Oil. Productivities on the order of 11.3 g PP/mmol Ti/hr (8.8 g PP/g total catalyst) are reported. The 20% of the polymer thus produced, which was soluble in hot isooctane, exhibited an IR syndiotactic crystallinity index of only 0.5 while the polymer which isn't soluble in hot isooctane exhibited an IR syndiotactic index of nearly zero, i.e. it is isotactic. Similar results are reported for VCl.sub.3.
U.S. Pat. No. 4,335,225, mentioned above, discloses a fractionable elastic polypropylene which is said to have an isotactic content of 55% or less and also to contain some syndiotactic and atactic polypropylene. This patent, and its companions on the catalyst system for making this elastic polypropylene, contain much information about elastic-type polypropylene compositions, although the researchers at Montecatini, especially including Giulio Natta, produced some polypropylene compositions which exhibited some of the characteristics of elastomeric compositions. Specifically, U.S. Pat. Nos. 3,175,999; 3,257,370 and 3,258,455 disclose polypropylene compositions which have some elastic-type properties.
Elastomeric polypropylene is different from the "normal" or more well known polypropylenes. These more well known types are crystalline and amorphous polypropylenes. It is normally accepted that crystalline polypropylene generally has the isotactic or syndiotactic structure and that amorphous polypropylene generally has considerable atactic structure. Giulio Natta's U.S. Pat. Nos. 3,112,300 and 3,112,301 describe isotactic polypropylene and give structural formulae for is and syndiotactic polypropylene. The former is a straight chain of propylene units wherein the methyl groups are all aligned on one side of the polymer chain. In the latter, the methyl groups alternate from one side of the chain to the other. In atactic polypropylene, the methyl groups are arranged randomly on the two sides of the chain.
Almost all of the polypropylene which is used commercially is crystalline isotactic polypropylene. These products are well known and have been the subject of many patents and articles. Amorphous polypropylenes, which have very little strength, are used commercially primarily in adhesives and asphalt additives.